In recent years geoexchange heating and cooling systems have become increasingly popular for new and existing buildings. Conventional geoexchange heating and cooling systems are typically based on the concept of using a geoexchange working fluid flowing through geoexchange piping installed below the ground surface to exchange heat to and from the ground mass surrounding the underground geoexchange piping. Geoexchange piping installations have typically been used either in horizontally oriented buried piping loops, or vertically oriented geoexchange piping loops. In many applications, particularly for use by large multistory buildings and/or closely spaced urban buildings, vertically oriented geoexchange piping installed in vertically drilled boreholes is the only possible option for geoexchange pipe fields, due to the length of piping required and the small available space for installation, particularly in urban areas.
However, conventional borehole drilling techniques and equipment may in many cases not be well suited to installation of vertical geoexchange boreholes for several reasons. Firstly, large multistory buildings may typically require relatively large installed lengths of geoexchange piping, requiring multiple relatively deep boreholes oriented in a grid covering a significant portion of the footprint of the building in order to achieve the required installed piping lengths. Accordingly, for geoexchange system installation in newly constructed buildings, geoexchange boreholes must either be installed under the footprint of the building before construction which typically results in expensive delay of foundation construction and typically difficult access to the bottom of an excavation for drilling equipment. Alternatively for a new building or for all cases of retrofit installation of geoexchange systems in existing buildings, geoexchange boreholes would need to be drilled through the existing foundation slab of the building.
Unfortunately, conventional borehole drilling systems are typically designed for use in largely open areas without strict headroom limits or confined spaces encountered in the bottom levels of most existing and new multistory buildings, which in many cases are reserved for parking garages with less than 7 to 8 foot ceiling heights and confined spaces between walls or pillars. Many conventional borehole drilling systems capable of drilling boreholes through varied hard ground conditions to the several hundred foot depths desirable for modern geoexchange system installations may typically use drill mast lengths of 10 to 40 or more feet, and may be mounted on large truck or tracked rig platforms which cannot access the lower levels of a building.
Further, many conventional borehole drilling systems may typically require use and disposal of large volumes of drilling fluids such as water or drilling mud during drilling, which may be uneconomic or improper for onsite disposal at an urban site, in addition to being potentially messy or hazardous to others in an urban environment. Accordingly, there remains a need for a geoexchange drilling system and corresponding drilling method which address some of the shortcomings of the drilling systems and methods known in the prior art.